The invention concerns a split meal cannula with at least one predetermined break line extending lengthwise, but preferably concerns a split cannula with two predetermined break lines extending lengthwise. The invention also concerns a process for the production of at least one predetermined break line extending in the lengthwise axis of a split cannula by processing of an extendable or extended tube.
So-called "split cannulas," which have predetermined break lines along the long axis of the cannula, are required in medicine, for example to introduce catheters (DE-C 2 104 211). These predetermined break lines are designed to offer the possibility, after insertion of the cannula and of the catheter that is inserted through it, for disassembling the cannula by hand into two pieces after it is pulled out. Disassembly needs to be possible with as little force as possible, while at the same time ensuring that "ripping" occurs over the entire length, in other words so that a portion of the cannula does not break off. This problem can occur, however, if the walls within the predetermined break lines do not have well-defined residual wall thicknesses. This can also cause one half of the cannula to bend, making further handling very problematical.
The predetermined break lines of known split cannulas are produced by metal-cutting processes, e.g. by milling. Because of the danger of infection from diseases such as AIDS, the user specifies that the cannulas must be free of sharp edges or burrs.
As already mentioned, the residual wall thicknesses within the predetermined break lines, which may be only a few hundredths of a millimeter thick, must also be uniform over the length of the cannula. In particular, the residual wall thicknesses of the opposite predetermined break lines must be identical, to permit easy and homogeneous ripping.
Complex manufacturing processes and regular destructive testing of finished split cannulas are needed in order to meet all these criteria. Since, in addition, manufacturing and handling are performed manually, production costs are high.